Effect of oxygen on denitrification in continuous chemostat culture withComamonas sp SGLY2

Continuous cultures ofComamonas sp SGLY2 were grown anaerobically prior to establishing steady states at different oxygen flow rates. At a low oxygen transfer rate, no dissolved oxygen accumulated in the medium and all nitrate was reduced to dinitrogen. Concurrently with the increase of dissolved oxygen concentration in the liquid phase, the rate of denitrification decreased. However, at a dissolved oxygen concentration near saturation (33 mg L^–1), a part of the electron flow always diverted to nitrate with production of dinitrogen: the aerobic denitrification rate was equivalent to 35% of that calculated under anaerobic conditions. These experiments reflected the co-utilization of oxygen and N-oxides and the production of dinitrogen, up to saturated conditions, which implied synthesis and activity of the four denitrifying enzymes under various aeration conditions.     

Production of chitinolytic enzymes from a novel species ofAeromonas

A bacterial strain secreting potent chitinolytic activity was isolated from shrimp-pond water by enrichment culture using colloidal crab-shell chitin as the major carbon source. The isolated bacterium, designated asAeromonas sp No. 16 exhibited a rod-like morphology with a polar flagellum. Under optimal culture conditions in 500-ml shaker flasks, it produced a chitinolytic activity of 1.4 U ml^–1. A slightly higher enzymatic activity of 1.5 U ml^–1 was obtained when cultivation was carried out in a 5-liter jar fermentor using a medium containing crystalline chitin as the carbon source. The secretion of the enzyme(s) was stimulated by several organic nitrogenous supplements. Most carbon sources tested (glucose, maltose, N-acetylglucosamine, etc) enhanced cell growth, but they slightly inhibited enzyme secretion. Glucosamine (0.5% w/v) severely inhibited cell growth (16% of the control), but it did not significantly affect enzyme secretion. The production of chitinolytic enzymes was pH sensitive and was enhanced by increasing the concentration of colloidal chitin to 1.5%. The observed chitinolytic activity could be attributed to the presence of -N-acetylglucosaminidase and chitinase. Chitinase was purified by ammonium sulfate fractionation and preparative gel electrophoresis to three major bands on SDS-PAGE. An in-gel enzymatic activity assay indicated that all three bands possessed chitinase activity. Analysis of the enzymatic products indicated that the purified enzyme(s) hydrolyzed colloidal chitin predominantly to N,N-diacetyl-chitobiose and, to a much lesser extent, the mono-, tri, and tetramer of N-acetylglucosamine, suggesting that they are mainly endochitinases.     

The use of arbuscular mycorrhizae to control onion white rot (Sclerotium cepivorum Berk.) under field conditions

 A field experiment was carried out to determine the effects of the inoculation of onion (Allium cepa L.) with Glomus sp. Zac-19 on the development of onion white rot (Sclerotium cepivorum Berk.) and on onion production. Mycorrhization delayed onion white rot epidemics by 2 weeks and provided a significant protection against the disease for 11 weeks after onion transplanting, as compared with nonmycorrhizal controls. Mycorrhizal plants showed an increase of 22% in yield, regardless of the presence of the white rot pathogen. Accepted: 8 January 1996     

青海湖裸鲤寄生舌状绦虫的空间格局研究

舌状绦虫裂头蚴只寄生在体长小于２２０ｍｍ的青海湖裸鲤中,其种群在宿主种群中呈聚集分布。其聚集分布的强度随寄生虫种群平均密度的增加而降低。由于舌状绦虫在宿主体腔生长,产生明显的空间拥挤效应,可能导致宿主死亡或被食鱼鸟类捕食而转移到终末宿主中。在体长小于１２０ｍｍ的宿主中,密度依赖的死亡过程可能是使聚集强度降低的原因;而体长１４０－２００ｍｍ的鱼中,则是非密度依赖的全死过程使聚集强度增加．     

云南元谋小河地区古猿地点的小型猿类化石

本文记述的云南元谋小河地区古猿地点发现的一种小型猿类。它的牙齿形态比晚中新世的禄丰粗壮池猿进步。而牙齿的某些形态介于粗壮池猿和现生长臂猿之间,它的发现为探讨现生长臂猿的起源与进货提供了新的化石依据。依哺乳动物群的初步研究,其时代稍晚于禄丰古猿地点的时代。鉴于它的形态特征和地史分布,作者将它订为一新属新种：进步滇猿Ｄｉａｎｏ ｐｉｔｈｅｃｕｓ ｐｒｏｇｒｅｓｓｕｓ ｇｅｎ．ｅｔ ｓｐ．ｎｏｖ。     

凤眼莲根分泌物氨基酸组分对根际肠杆菌属F2细菌的趋化作用

凤眼莲(Eichhornia crassipes)的根分泌物中含有Met等多种氨基酸,其中Met、GABA、Gly、Ala、Asp、Ser、Val和Leu(10^-7～10^-2mol·L^-1)均对凤眼莲的根际肠杆菌属F₂(Enterobacter sp.F₂)细菌有强烈的正趋化作用;Glu、Thr和His(10^-7～10^-3mol·L^-1)也对该菌有一定的正趋化作用;而Lys、Cys、Arg、Tyr、Pro、Asn、Gln、Ile、Phe和Typ则对该菌表现出一定的负趋化作用.对细菌的正趋化作用存在一个趋化物的最适浓度范围.具有正趋化作用的氨基酸在凤眼莲根际的浓度都较高,而具有负趋化作用的浓度则较低,这正是凤眼莲与该根际细菌结合为根际微生态系统的原因之一.     

Two new species of the genusAmblyeleotris (Pisces: Gobiidae) from the Ryukyu Islands,Japan

Two new shrimp-associated gobies,Amblyeleotris yanoi sp. nov. andA. masuii sp. nov. are described on the basis of specimens from Iriomote-jima Island and Okinawa-jima Islands, Okinawa Prefecture, Japan.A. yanoi is distinguished from other members of the genus by the combination of the following characters: 14 anal fin soft rays, 19 pectoral fin rays, 97–103 longitudinal scales, a candle flame-shaped marking on the caudal fin, a very low membrane connecting the pelvic fins and absence of a ventral frenum.A. masuii differs from all other congeners by having 92–97 longitudinal scales, the length of the interpelvic connecting membrane relative to the longest pelvic fin ray (0.43–0.66), black blotches on the sides of the chin, and blue spots on the opercle and preopercle.     

Primary Structure and Phylogenetic Relationships of Glyceraldehyde-3-Phosphate Dehydrogenase Genes of Free-Living and Parasitic Diplomonad Flagellates

ABSTRACT. Complete nucleotide sequences have been established for two genes (gap1 and gap2) coding for glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) homologs in the diplomonad Giardia lamblia. In addition, almost complete sequences of the GAPDH open reading frames were obtained from PCR products for two free-living diplomonad species, Trepomonas agilis and Hexamita inflata, and a parasite of Atlantic salmon, an as yet unnamed species with morphological affinities to Spironucleus. Giardia lamblia gap 1 and the genes from the three other diplomonad species show high similarity to each other and to other glycolytic GAPDH genes. All amino-acyl residues known to be highly conserved in this enzyme are also conserved in these sequences. Giardia lamblia gap2 gene is more divergent and its putative translation reveals the presence of a cysteine and serine-rich insertion resembling a metal binding finger. This motif has not yet been noted in other GAPDH molecules. All sequences contain an S-loop signature with characteristics close to those of eukaryotes. In phylogenetic reconstructions based on the derived amino acid sequences with neighborjoining, parsimony and maximum-likelihood methods the four typical GAPDH sequences of diplomonads cluster into a single clade. Within this clade, G. lamblia gap1 shares a common ancestor with the rest of the genes. The latter are more closely related to each other, indicating an early separation of the lineage leading to the genus Giardia from the lineage encompassing the morphologically less differentiated genera, Trepomonas, Hexamita and that of the unnamed species. This result is discordant with the orthogonal evolution of diplomonads suggested on the basis of comparative morphology. In neighbor-joining reconstructions G. lamblia gap2 occupies a variable position, due to its great divergence. In parsimony and maximum likelihood analysis however, it shares a most recent common ancestor with the typical G. lamblia gap1 gene, suggesting that it diverged after the separation of the Giardia lineage. The position of the diplomonad clade in broader phylogenetic reconstructions is firmly within the typical cytosolic glycolytic representatives of GAPDH of eukaryotes.     

Natural Occurrence ofChondrostereum purpureumin Relation to Its Use as a Biological Control Agent in Canadian Forests

The incidence of natural fructification ofChondrostereum purpureumwas estimated quantitatively on southern Vancouver Island during two winter seasons in randomly located 1000-m²plots and compared with potential added fructification that might occur as a result of using the fungus to control stump-sprouting of hardwood weeds in young forest stands. Fructification was surveyed in forests as well as in urban or agricultural areas by estimating the surface areas of woody substrates covered with basidiocarps. In addition to random plots, estimates were made also in locations where the fungus would be expected to occur (woodpiles, silvicultural thinnings, and killed trees). Basidiocarps were found throughout the area in various types of forest cover as well as in urban or agricultural situations. The amount of added fructification through the use of the fungus as a biological control agent was determined from inoculated plots as well as from calculated stump-surface areas developed from published stand-density data. Added fructification was multiplied by a factor representing the maximum biological control frequency in order to compare added fructification with natural fructification values. From the various calculations, it was determined that the added fructification ofC. purpureumis of the same order of magnitude as naturally occurring levels or even lower. In addition, there is a distinct geographical separation between predominantly forestry and predominantly settled areas where fruit and ornamental trees are cultivated. Accordingly, it was concluded that using the fungus as a biological control agent in forestry is not likely to pose a significant threat to fruit growing and commercial forests.     

The impact of mycorrhizal colonization upon nitrogen source utilization and metabolism in seedlings of Eucalyptus grandis Hill ex Maiden and Eucalyptus maculata Hook

Analysis of soil solution from forest sites dominated by Eucalyptus grandis and Eucalyptus maculata indicates that soluble forms of organic nitrogen (amino acids and protein) are present in concentrations similar to those of mineral nitrogen (nitrate and ammonium). Experiments were conducted to determine the extent to which mycorrhizal associations might broaden nitrogen source utilization in Eucalyptus seedlings to include organic nitrogen. In isolation, species of ectomycorrhizal fungi from northern Australia show varying abilities to utilize mineral and organic forms of nitrogen as sole sources. Pisolithus sp. displayed strongest growth on NH₄⁺, glutamine and asparagine, but grew poorly on protein, while Amanita sp. grew well both on mineral sources and on a range of organic sources (e.g. arginine, asparagine, glutamine and protein). In sterile culture, non-mycorrhizal seedlings of Eucalyptus grandis and Eucalyptus maculata grew well on mineral sources of nitrogen, but showed no ability to grow on sources of organic nitrogen other than glutamine. In contrast, mycorrhizal seedlings grew well on a range of organic nitrogen sources. These observations indicate that mycorrhizal associations confer on species of Eucalyptus the ability to broaden their resource base substantially with respect to nitrogen. This ability to utilize organic nitrogen was not directly related to that of the fungal symbiont in isolation. Seedlings mycorrhizal with Pisolithus sp. were able to assimilate sources of nitrogen (in particular histidine and protein) on which the fungus in pure culture appeared to grow weakly. Experiments in which plants were fed ¹⁵N-labelled ammonium were undertaken in order to investigate the influence of mycorrhizal colonization on the pathway of nitrogen metabolism. In roots and shoots of all seedlings, ¹⁵N was incorporated into the amide group of glutamine, and label was also found in the amino groups of glutamine, glutamic acid, γ-aminobutyric acid and alanine. Mycorrhizal colonization appeared to have no effect on the assimilation pathway and metabolism of [¹⁵N]H₄⁺; labelling data were consistent with the operation of the glutamate synthase cycle in plants infected with either Pisolithus sp. (which in isolation assimilates via the glutamate synthase cycle) or Elaphomyces sp. (which assimilates via glutamate dehydrogenase). It is likely that the control of carbon supply to the mycorrhizal fungus from the host may have a profound effect on both the assimilatory pathway and the range of nitrogen sources that can be utilized by the association.